The present invention relates generally to micro-machined convective accelerometers, and more specifically to multiple axis thermal accelerometers capable of being formed on a single chip.
U.S. patent application Ser. No. 11/125,759 filed May 10, 2005 entitled Z-AXIS THERMAL ACCELEROMETER and assigned to the same assignee of the present invention (the '759 application) discloses a thermal accelerometer that allows up to three axes of acceleration sensing. The disclosed thermal accelerometer comprises a thermal acceleration sensor including a substrate having a substantially planar surface defined by X and Y coordinate axes, at least one cavity formed in the substrate, at least one heater element, first and second temperature sensing elements, and an internal reference voltage. The heater element is suspended over the cavity in the X-Y plane, and the first and second temperature sensing elements are disposed along either the X-axis or the Y-axis on opposite sides of and at substantially equal distances from the heater element. The thermal accelerometer further includes amplification circuitry operative to receive signals representing a differential temperature detected by the first and second temperature sensing elements, in which the differential temperature is indicative of a sensed acceleration along the X or Y-axis. The amplification circuitry is also operative to receive signals representing a common mode temperature detected by the first and second temperature sensing elements, in which the common mode temperature is indicative of a sensed acceleration along the Z-axis. The amplification circuitry produces output voltages representative of the magnitudes of acceleration in the X, Y, and Z directions. As disclosed in the '759 application, the thermal accelerometer may be implemented using fabrication techniques that are compatible with CMOS and bipolar processes.
Although the thermal accelerometer disclosed in the '759 application can be successfully employed to obtain up to three axes of acceleration sensing, there is an increasing need for single chip multiple axis thermal accelerometers that provide enhanced performance over existing multi-axis thermal accelerometer devices. Such enhanced thermal accelerometer devices would include thermal acceleration sensors having reduced temperature coefficients, and would produce output voltages exhibiting reduced DC offset and drift. Heretofore, the increasing need for single chip multiple axis thermal accelerometers enhanced for higher performance has not been fully met. It would be-desirable to have single chip multi-axis thermal accelerometers that address this requirement.